1. Field of the Invention
This invention relates to a real image mode finder optical system which is suitable for compact cameras such as photographic cameras and video cameras.
2. Description of the Related Art
For finder optical systems used in compact LS (lens shutter) cameras, real image mode finder optical systems of a Keplerian type (set forth, for example, in U.S. Pat. No. 5,184,252), instead of Albada and inverse Galilean types, have recently come into frequent use. In each of these conventional real image mode finder optical systems, its half field angle of incidence on the finder is no more than about 15.degree. even with high finder magnification, while its finder magnification is only about 0.4.times. even with a wide finder field. Thus, no real image mode finder optical system has been made to combine the high finder magnification with the wide finder field.
Such high finder magnification in the conventional real image mode finder optical system has been obtained in the following limited way: by either relatively increasing the focal length of an objective lens compared with that of an eyepiece or relatively diminishing the focal length of the eyepiece compared with that of the objective lens. If, however, the focal length of the objective lens is increased in the above way, an intermediate image height must also be increased, which fact makes it difficult to secure compactness of the optical system and correction for aberrations. If, on the other hand, the focal length of the eyepiece is reduced, the angle of emergence of the finder becomes great, although the intermediate image height need not be increased. Consequently, if an attempt is made to ensure the distance between the last surface of the eyepiece and an eyepoint in a relatively long range, the maximum beam diameter at the eyepiece will increase because the diameter of an exit pupil is constant. Thus, the problem has arisen that it is difficult to ensure a space required for an eyepiece optical system including a reflecting member for erecting an image.